The present invention relates to vaporisers and in particular to vaporisers for medical purposes.
Frequently, volatile liquid agents need to be administered to patients in vapour form for a variety of medical purposes. For example, anaesthetic vaporisers are devices for mixing the vapour of a volatile liquid anaesthetic agent with a carrier gas (which term is to be understood to include gas mixtures) for subsequent administration to a patient.
Anaesthetic vaporisers are known in which the carrier gas supplied to the vaporiser is divided into two streams. One stream is directed through a vaporising chamber where it becomes enriched with the vapour of the anaesthetic. The second stream by-passes the vaporising chamber. The two streams subsequently reunite downstream of the vaporising chamber and then pass through an outlet of the vaporiser for administration to the patient.
Such anaesthetic vaporisers are know generally as "by-pass" vaporisers and the concentration of anaesthetic vapour in the gas leaving the vaporiser is frequently controlled by mechanical means such as thermally sensitive valve arrangements and restrictor valves placed in one or both of the streams.
Such valve arrangements frequently require very accurate machining and calibration and although effective are extremely expensive to manufacture. Furthermore, known valve arrangements have tended to be large and heavy.